The present invention relates to an improved spray suppression system for an air cushion craft. Such craft are supported by a pressurized air cushion contained within a depending skirt installed about the bottom periphery of the craft's hull. The skirt consists of a peripheral bag fixed to the hull and a bow seal, a stern seal, and side seals extending downward from the bag. The bag is generally inflated by pressurizing air from the air cushion supply. Once inflated it acts as a fluid distribution medium and a resilient support for the craft to absorb and distribute shock. The seal assembly defines the air cushion containment structure and as such must be delicately balanced to provide, pitch and role stability, low drag, structural integrity, and restoring moment in addition to its basic role of air cushion containment.
The seal is constructed as a continuous assembly of contiguous fingers depending from the bag about the lower periphery of the craft. The fingers define individual cells open at the bottom and communicating with the interior of the bag at the top. To provide structure to the otherwise flexible element, each finger is pressurized by air from the peripheral bag. As such seals dip into the water, there is a pressure increase in the cell which generates a restoring moment at that position to stabilize the craft. The finger may be maintained at a pressure which is greater than the air cushion pressure.
The seal system is designed to define an area of supporting pressure under the craft, but does allow the escape of air from the cushion outward from the craft. This rapid movement of air outward through the gap between the seal and the sea creates significant turbulence and large amounts of spray and mist are generated. This spray creates problems of visibility and salt water infiltration into operating systems.
U.S. Pat. No. 4,223,755 illustrates an attempt to suppress spray in an air cushion vehicle. It comprises a flexible curtain installed downward over the outer surface of the seal system. Escaping air and mist is captured by the curtain which billows outward under pressure from the turbulent air. The air is allowed to escape through the holes in the upper area of the curtain. This type of apparatus has proved ineffectual in containing the spray because of the difficultly in maintaining a consistent curtain. A ballast was inserted in an attempt to restrain upward movement of the lower edge of the curtain, but this did not substantially improve the spray suppression performance. In addition, in this type of design, a significant penalty is paid in increased drag. Also collapse of the curtain, eliminates spray suppression along an entire segment of the vehicle.
It has been found that spray is generated due in large amount to the turbulence created as the cushion air escapes from its relatively high pressure to ambient pressure external to the craft. It is therefore the purpose of this invention to reduce the generation of fog and fine mist spray by reducing the differential pressure in the immediate vicinity of the air cushion boundary, to trap and redirect the remaining spray horizontally over the water surface and to enhance craft performance in the process.